Space fumigation system

ABSTRACT

THE FUMIGATION OF ENCLOSED SPACES, AND PARTICULARLY TOBACCO WAREHOUSES, IS ACCOMPLISHED BY THE INJECTION AT PREDETERMINED INTERVALS OF A SOLUTION OF A DIALKYL HALOVINYL PHOSPHATE OF OF PYRETHRUM IN A TRICHLOROETHANE, UTILIZING AN AUTOMATIC DISPENSING SYSTEM INCLUDING MEANS FOR SUPPLYING INSECTICIDE SOLUTION, A SOURCE OF COMPRESSED AIR, AN INSECTICIDE DISTRIBUTION CONDUIT PROVIDED WITH A SERIES OF SIPHON MEMBERS EACH FITTED WITH A PNEUMATIC ATOMIZING SPRAY NOZZLE AND CONNECTED TO THE COMPRESSED AIR SUPPLY TO FORM A SIPHON SPRAY SYSTEM FOR DISTRIBUTION OF THE INSECTICIDAL LIQUID IN FINELY DISPERSED CONDITION.

United States Patent [72] Inventors Jesse Douglas Rollow, Jr.

' 6106 Cromwell Drive, Washington, D.C.

20016; Constant Roosevelt Ray, 2204 Colwyn Road, Richmond, Va. 23229(21] Appl. No. 784,800 [22] Filed Dec. 18, 1968 [45] Patented June 28,1971 [54] SPACE FUMIGATION SYSTEM 7 Claims, 4 Drawing Figs.

[52] U.S. Cl 239/550, 21/58, 222/4, 222/204, 239/70, 239/424 [51} 1nt.ClB05b 1/14 [50] Field of Search 21/2,58, 106, 107, 108, 109; 2391266,268, 550, 551; 222/4, 482, 565, 204

[56] References Cited UNITED STATES PATENTS 762,014 6/1904 Wittbold239/550 928,038 7/1909 Fusch 21/108X 1,056,094 3/1913 Gilman 239/550X1,658,220 2/1928 Binks 239/550X 2,473,684 6/1949 Howard. 21/1083,062,454 11/1962 Cocks 239/550X 3,137,446 6/1964 Senichi Masuda239/551X 3,370,571 2/1968 Knapp 43/132X Primary Examiner-Morris O. WolkAssistant Examiner-Joseph T. Zatarga At!orney-Hugo E. WeisbergerPATENTED JUN28 IBM 3, E387 9 i3 2 INVENTORS JESSE DOUGLAS ROLLOW JR.cowsmm R. RAY

ATTORNEY SPACE FUMIGATION SYSTEM BACKGROUND OF THE INVENTION The controlof insects and other pests within large enclosed spaces such asbuildings, bins, and the like, in which there are stored commoditiessusceptible to insect attack is a matter of great economic importance.It is customary in the storage of tobacco leaves, and'especiallyflue-cured tobacco, to store this product for periods of as much asseven or eight years in tobacco warehouses. Such stored tobacco issubject to serious insect infestations, of which the most familiarexamples are those of the cigarette beetle, Lasioderma serricorne (F),and the tobacco moth, Ephestia elutella (Huebner). Early efforts tocontrol these two pests utilized mainly pyrethrum, applied either as apowder by dusting within the storage space, or in the form of an aerosoltogether with a highly refined volatile hydrocarbon oil as a carrier.

More recently it was found that tobacco, grains, and other storedcommodities could be protected against insect damage by fumigation ofthe storage areas with the vapors of a dialkyl halovinyl phosphate, thepreferred compound for this purpose being dimethyl 2,2-dichlorovinylphosphate (DDVP), also sold under the designation Dichlorvos. DDVP isknown to be particularly effective against the cigarette beetle and thetobacco moth and it had been proposed in prior art to apply thiscompound as a thermal aerosol either alone, or in percent solution in alight oil, from an automatic generator suspended above hogsheads oftobacco, utilizing an automatic timer and solenoid valve, set to releasea concentration of about 0.5 grams per 1,000 cubic feet daily in thelate afternoon just preceding the peak flight activity of the insect. Inaddition to the use of such carriers as deodorized kerosene, DDVP isalso applied in the form of an aqueous emulsion ofa solution of theinsecticide in a halogenated aliphatic hydrocarbon such as carbontetrachloride or tctrachloroethylene (perchloroethylene), and a processof this type is described in U.S. Pat. No. 2,968,59l. These previouslyemployed halogenated solvents have not been entirely satisfactory, however, owing to the large differential in vapor pressure between the DDVPand the solvent, problems in maintaining the DDVP in solution, and thetendency of the solvent to condense and to wet the tobacco leavesdirectly or by penetration into the hogsheads. Accordingly, there hasexisted a need for a suitable solvent which would be free from thesedrawbacks and which would not cause actual or potential damage to thetobacco or other commodities.

As indicated previously, it has been customary to apply DDVP either bydirect air pressure spraying ofits solutions, or as an aerosol or mistby means of mechanical or thermal fog generators. Thus in one systemdeveloped by the US. Department of Agriculture, an automatic dispensingunit applies a metered amount of the insecticide at a specific time fora repeated number of discharges. The system consists of a pressurizedcylinder controlled by a solenoid valve energized by a central clocktimer. Another known system is that disclosed in US. Pat. No. 3,209,950,wherein a metered amount ofinsecticide is dispensed from an aerosol typecontainer in which it is stored under pressure together with afluorocarbon propellent, the dispensing being regulated by the action ofa solenoid valve and a clock mechanism. These systems, in which thehighly toxic insecticide is constantly maintained under considerablepressure, have the major disadvantage that leakage may occur, therebyendangering operators or other persons entering the warehouse betweenapplication sequences. They also require periodic changes or renewals ofpressure supply cylinders or aerosol bottles. Moreover in the case ofthe aerosol bottles the discharge pressure may drop below the ef'fective level as the container contents near exhaustion. Finally, as isthe case with most pressurized systems, they are cumbersome in operationand expensive to maintain. There has accordingly existed a long-feltneed for a liquid dispensing system and particularly an insecticidedispensing system in which the liquid or the insecticidal solution wouldbe distributed from a central supply source and dispensed in spray format a plurality of points of application, the liquid or the insecticidalsolution being at ordinary atmospheric pressure, and with suitable meansprovided for automatic dispensing and spraying.

GENERAL DESCRIPTION OF THE INVENTION In accordance with the presentinvention, there is provided a novel system for the distribution anddispensing ofliquids, such as insecticidal solutions, within an enclosedspace. The system will be described with particular reference to itsapplication in warehouses for the storage of tobacco, but it is to beunderstood that such description is for purposes ofillustration only,and that the principles of the invention are applicable to all types ofinstallations for dispensing not only insecticidal solutions, but othervolatile or siphonable liquids.

In accordance with another aspect of the invention, there is provided anovel insecticide composition and process of applying the same, saidinsecticide comprising a solution of a dialkyl halovinyl phosphate or ofpyrethrum in a trichloroethane. This insecticidal solution dimethylvolatility characteristics which enable it to be successfully utilizedin the dispensing system of the invention, and at the same time, thedispensing system, operating as it does with the insecticidal solutionat atmospheric pressure, is especially suited for handling this type ofvolatile insecticide.

The novel insecticidal composition of the present invention comprises asolution of a dialkyl halovinyl phosphate or of pyrethrum in atrichloroethane. The trichloroethane is preferablyl,l,l,-trichloroethane (methyl chloroform), CH C-Cl;,, a colorlessliquid, insoluble in water, boiling point 75 C., specific gravity 1.325.This solvent possesses very favorable volatility characteristics,forming a persistent mist, but with no tendency to condense on thetobacco or other commodity being treated. Alternatively there may beemployed as a solvent, the compound l,l,2-trichloroethane (vinyltrichloride), CH-Cl -CH Cl, a colorless liquid, boiling point ll3.7 C.,specific gravity 1.4432, but the volatility characteristics of thissolvent are less favorable.

The preferred dialkyl halovinyl phosphate is dimethyl 2,2- dichlorovinylphosphate. However other compounds of this class which may be employedinclude: diethyl-2,2-dichlorovinyl phosphate, dimethyl 2-chlorovinylphosphate, di-sec-butyl 2,2-dichlorovinyl phosphate, dimethyl2,2-dibromovinyl phosphate, dimethyl l,2-dibromo-2,2-dichloroethylphosphate, and dimethyl l,2-dibromo-2-chloroethyl phosphate.

The concentration ofDDVP or equivalent insecticide of the same type liesin the range ofabout 10 percent by weight up to the limit of solubility,preferably between about 10 percent and about 20 percent. A minorportion of the trichloroethane may be replaced by a diluent, such as,for example, a highly refined volatile hydrocarbon, e.g. deodorizedkerosene. The clear solution is characterized by rapid evaporation ofthe solvent, with both the active ingredient and the trichloroethanevaporizing promptly upon leaving the spraying nozzle, and with completeavoidance of clogging difficulties.

It has been found, in accordance with the present invention, that theaddition to the DDVP-trichloroethane combination of from about 0.01percent to about 1 percent by weight of an alkali metal or alkalineearth metal salt of an alkyl carboxylic acid having between about fourand about l2 carbon atoms serves to minimize corrosion of metal nozzlesand to stabilize the solution. Samples of such acids include butyric,octoic, and lauric acids. The preferred acid is one containing eightcarbon atoms, and may be either straight chain or branched in structure,for example octoic acid. Examples of alkali metals include sodium andpotassium, while examples of alkaline earth metals include calcium andbarium. The preferred additive is calcium octoate, in an amount of fromabout 0.25 to about 1 percent, and preferably about 0.5 percent byweight.

In accordance with the practice of the invention, the dialkyl halovinylphosphate solution, prepared as described, is in jected into the spaceto be fumigated in the form of a fog or mist of finely dividedparticles, preferably using the spraying system described more fullybelow. The preferred practice involves application of dosage rate of thedialkyl halovinyl phosphate, for example DDVP, at a level of 0.5 gramsper 1,000 cubic feet, daily. The insecticide is applied each afternoonduring the twilight hours when the insects are flying. The system isdesigned so that the recommended dosage is applied during a period ofapproximately 1 to 8 minutes each day. Particle size of the fog or mistis of importance, although not critical, and will advantageously liepredominantly in the range of about 1 to about 40 microns, preferablyfrom about 1 to about 15 microns.

Where pyrethrum is employed as the active insecticidal ingredient, it isin solution in a concentration of about 1 percent by weight in atrichloroethane solvent. A suitable formulation is a solution of 1percent pyrethrum, 50 percent 1,1,1- trichloroethane, and 49 percentUltransene (deodorized refined kerosene), all by weight, lf desired, asmall amount of a synergist, such as piperonyl butoxide, may beincluded.

1f the insecticidal solutions of the invention are to be applied inemulsion form, a suitable surface-active agent may be incorporatedtherein, in accordance with conventional practice. There may also beincorporated suitable antioxidants and other types ofstabilizers.

DESCRIPTION OF THE PREFERRED EMBODIMENT The practice of the inventionand the operation of the novel space fumigation system will be morereadily understood by reference to the accompanying drawings, which areillustrative ofa presently preferred embodiment, and in which:

FIG. 1 is a vertical sectional view through a storage warehouse orchamber, showing the general organization of the pneumaticinsecticide-spraying system;

H6. 2 is a view, partly in section, showing the arrangement of thecompressed air and liquid supply lines, siphon tube and spray nozzlemounting; and

H6. 3 is a sectional view ofa siphon spray nozzle.

FIG. 4 is a front elevation of the exit portion of the spray nozzleshowing the liquid discharge orifice surrounded by the annular airdischarge nozzle.

Referring now to the drawings, a building structure to be fumigated,such as a tobacco warehouse, is depicted diagrammatically at 10. Thewarehouse has walls 11, roof structure 12, and floor 13. Positioned onthe floor in the interior of the warehouse 10 are hogsheads 14 oftobacco, shown generally. The space fumigation system comprises a supplytank 15 for holding insecticidal solution, which is kept filled from acentral source, not shown, via inlet 16. Extending in a horizontalposition from outlet 17 of the supply tank is a conduit 18, which may bemade of any suitable material, such as stainless steel or a plastic suchas polypropylene or polytetrafluoro ethylene (Teflon). At selectedintervals there extend vertically upward from conduit 18, a plurality ofsiphon conduits 19, through which the liquid is induced to rise by theaction of the compressed air as described below. These siphon membersmay be of any suitable height, depending upon the specific gravity andthe flow rate of the liquid being dispensed. In a typical installationthe liquid conduit 18 may range in inside diameter from aboutthree-eighths inch to about 1 inch, depending upon the flow rate and thenumber ofspray nozzles to be supplied. The siphon conduits are of aheight sufficient to provide a siphon action for the liquid being used,and their height will typically range from about 3 inches to about 12inches.

At its upper end, each siphon member 19 is connected to the liquid inletportion 28 ofa siphon-type pneumatic atomizing spray nozzle 20, anembodiment ofwhich is shown in more detail in FIGS. 3 and 4. The spraynozzle comprises a body portion 20 provided at its lower end with aninlet 28 which may be threaded and which leads to a liquid dischargenozzle 29 which terminates in a narrow liquid discharge orifice 30. Theliquid discharge orifice 29 is provided with a screw plug 31 to permitcleaning or insertion of a needle control attachment when necessary. Atthe upper end of body member 20 there is an air inlet 21 which connectswith a plurality of air ports 33, the air being first forced through anintermediate gasket 34 which is provided with a multiplicity of openingswhich serve to distribute the compressed air so that it surrounds liquidorifice 30 in a chamber provided by cap 35, which has in its center anopening 36 of a diameter sufficient to form an annular air nozzle 37.The flow of air through air nozzle 37 induces a flow of liquid throughliquid orifice 30, and forms a fine spray or mist, which is transmittedto the space surrounding the spray nozzle.

Increasing air pressure at any given liquid pressure decreases liquidparticle size, and decreasing air pressure increases liquid particlesize. It will further be apparent that the spray particle size will bedependent upon the relationship between the inside diameter of theliquid orifice, and the outside diameter of the liquid orifice in itsrelation to the diameter of the annular air nozzle opening. For theinsecticidal solutions of the invention, the liquid orifice size willadvantageously range from about 0.016 inch to about 0.100 inch insidediameter; the outside diameter will advantageously range from about0.050 inch to about 0.150 inch. The air nozzle diameter willcorrespondingly range from about 0.064 inch to about 0.180 inch insidediameter.

There is connected to the airinlet portion 21 of each spray nozzle 20 aflexible conduit 22, a multiplicity of which leads from an air supplypipe 42 which has dimensions similar to those of the liquid supplyconduit. The liquid supply conduit 18 is suspended from roof 12 byhanger members 40, as shown in FIG. 1, while the air supply conduit 42is suspended from the roof 12 by hanger members 41, at a height whichplaces it at approximately the same level, or near the level of thespray nozzles 20. The respective conduits and fittings therefor, when ofplastic material, provide low cost, flexibility, high tensile strength,resistance to corrosion, and ease ofinstallation.

Compressed air or other gas is supplied to the system at any desiredpressure, for example between about 10 and 50 lbs. per sq. inch,preferably 30-35 lbs. per sq. inch, from a compressor and compressed airstorage tank shown generally at 44. The system is rendered substantiallyautomatic by the inclusion in the air supply line leading fromcompressor 44, of a solenoid valve 45 of any suitable type, which isactuated by a timer 46. The solenoid valve serves to turn the air supplyon and off electrically, being normally closed and open when actuated bythe timer. The timer 46 is preferably of a type which will provide timeintervals between 1 second and '60 minutes, and which will stop thesolenoid valve at a preselected time. There may also be included in theair supply line an air filter 47, and an air pressure regulator andgauge 48.

In the operation of the fumigating system, a supply of insecticidalsolution, such as a solution of DDVP or pyrethrum in1,1,l-trichloroethane, is maintained in supply tank 15 and flows throughconduit 18 into siphon members 19. The insecticide is dispensed by meansof compressed air supplied to the spray nozzles at selected timeintervals and at any desired rate. For example, the system may beadjusted to dispense approximately 0.5 grams daily of DDVP per 1,000cubic feet of storage space in approximately 2 minutes during thetwilight hours which correspond to maximum flight activity of theinsects. The timer is set for the required time and turned on at dusk.1t stops automatically and remains inactive until the following evening.

The following examples illustrate the composition and method of theinvention, but are not to be regarded as limit- EXAMPLE 1 Aninsecticidal solution of i,l.l-trichloroetharle containing 20 percent byweight of dissolved dimethyl 2,2-dichlorovinyl phosphate was prepared,in which there was incorporated 0.5 percent by weight of calciumoctoate. Utilizing the dispensing system described above, with airpressure at 35 lbs. per sq. inch, and adjusting the spray nozzles for aparticle size of ll microns, the solution was sprayed into the interiorof a tobacco warehouse containing stored tobacco at a rate of 0.5 gramsDDVP per 1,000 cubic feet of storage space for a period of 2 minutes.Tests showed that 98 percent of the sprayed particles had a particlesize below l5 microns. Destruction of cigarette beetle and tobacco mothinfestations was virtually complete.

EXAMPLE 2 b. a conduit for distribution of said liquid connected to saidcontainer and having connected therewith a plurality of upward extendingsiphon conduits;

c. a plurality of pneumatic atomizing spray nozzles for dispensing saidliquid mounted at the upper ends of said siphon conduits; and

d.' a source of compressed gas connected by means of an air conduit toeach of said spray nozzles whereby to draw said liquid into said spraynozzles and to expel the liquid therefrom in finely dispersed form.

2. The system of claim I in which said liquid and air conduits aresuspended in substantially horizontal position by means of hangermembers.

3. The system of claim 1 in which said liquid is at substantiallyatmospheric pressure.

4. The system of claim 1 which further includes a solenoid valvepositioned in the gas supply source to initiate or stop the flow of gasto said spray nozzles.

5. The system of claim 4 which further includes timing means forperiodically actuating said solenoid valve at predetermined periods oftime.

6. The system of claim 1 in which said system includes a body ofaninsecticidal solution.

7. The system of claim 6 in which said siphon conduits are of a heightsufficient to provide siphon action for said insecticidal solution.

